username='a'
passwd='a'
for i in range(2,5):
    print('请输入用户名：')
    u = input()
    print('请输入密码：')
    p = input()
    if username and passwd ==u and p:
        print('pass')
        break
    else:
        print('username or passwd not true')
        if i<4:
            print('pl try {} times'.format(i))
        else:
            print('pl call 110 for help! 呵呵')
